1. Field of the Invention
The present invention relates to continuous dyeing techniques for fibers and in particular to the carpet industry.
2. Description of the Prior Art
In the last several years, the carpet industry has seen a particularly rapid expansion, which is expected to continue in the foreseeable future. Between 1960 and 1970, U.S. carpet fiber production will have grown almost threefold compared with a slower, but nevertheless increasing, rate of growth in Europe. There are many reasons for this expansion. Increasing standards of living, the increasing introduction of relatively cheap, hard wearing, synthetic fibers and a marked tendency to employ carpeting to replace hard floor coverings in homes, schools, hospitals and offices, have all played their part. Tufted carpets have now almost completely replaced conventional woven types in the U.S.A. and a continuing trend in this direction is evident in Europe also, although at present only 50 percent of production is of tufted types.
World production of carpets now stands at some 560 million square yard p.a., of which the U.S.A. and European manufacturers produce about 55 and 35 percent respectively. The greatest rate of expansion in all countries lies in tufted carpets, for which nylon and acrylic fibers will be of prime importance. In Europe, and more particularly the U.K., however, viscose rayon is still widely used, in contrast to the U.S.A. In the U.S.A., however despite the advent of polyester and polypropylene, the share between the various fiber types seem unlikely to show any major change.
B. C. F. Nylon is the major fiber used in tufted carpets both in the U.S.A. and Europe and the bulk of these carpets are piece dyed on the winch. It is somewhat surprising that continuous dyeing techniques were not widely adopted in the U.S.A. until quite recently, and that the initial lead in this field has been mainly in the U.K. and Western Germany. Increasing usage is now being made of continuous dyeing techniques, however, which are not confined to piece dyeing only, but may also be employed for yarn and loose stock dyeing. Continuous dyeing of piece goods offers the greatest economy and flexibility in production, allows minimum stockholding of dyed fiber and affords the carpet produced to deliver the finished goods in the shortest possible time following the receipt of an order. These factors are particularly important as there is an increasing tendency to minimize capital tied up in stock, by the producer wholesaler and retailer alike, and for the customer (with the exception of contract work) to order simply from pattern books of specific shade ranges.
The continuous dyeing of tufted carpets is, in many ways, much more difficult, mechanically, than the continuous dyeing of fabrics. The stages involved are, however, the same, namely, the even impregnation of dye on the goods, than colour fixation, and finally washing and/or after treatment and drying. With tufted carpets the machinery must be constructed much more robustly since the goods, particularly in the wet state, have a considerably higher unit weight. Tufted carpets up to 15 ft. in width are now commonly produced, so that the pad-mangles, steamers etc., that are available for the processing of woven goods are generally inadequate for carpets. This led individual firms, who adopted continuous dyeing methods for carpets, to designing their own equipment. Recently, however, a number of complete processing units have become commercially available. These differ mainly in the techniques employed at the due impregnation stage.
Continuous dyeing systems lose much of their appeal if the goods to be dyed cannot be prepared continuously. They are even more attractive if no preparation at all is necessary. European practice is, in fact, to dye all carpets without any pre-scouring.
As previously indicated the stages involved in dyeing carpets continuously are:
1. Dye impregnation PA1 2. Dye fixation PA1 3. Washing off PA1 4. Drying
Dye impregnation is the part of the process that has received the greatest attention by machinery manufacturers since the uniform application of dye liquor across a 15 ft wide carpet without pile deformation presented new problems, and several solutions have been evolved.
Perhaps the least sophisticated, but nevertheless wellproven and versatile, method involves the pad/drain technique. Dye liquor is applied by padding the carpet without any squeezing action. After passing through the dye liquor the carpet travels in an inclined or vertical plane so that the downward flow of the liquor attains an equilibrium with the upward movement of the carpet. The pick-up attained is controlled by the distance, angle, and speed of carpet travel and by the type of carpet being processed.
Following more conventional techniques, it is possible to utilize special pad-mangles (operating on the "swimming" or "floating" roller principle) which give an even expression over the full width of the carpet. A continuous dyeing range operating in this way is that developed by Beloit-Kleinewefers. However, machines involving a squeezing action of this type tend to have limitations when used on certain carpet constructions (e.g. deeply sculptured designs, or with acrylic carpets when the crushed pile will tend to become set by steaming and subsequent rapid cooling in the washing-off section).
All the above methods, since these involve total immersion of the carpet in the dye liquor result, to varying degrees, in dyeing of the jute backing of the carpet, in addition to the carpet pile. On the other hand, the total immersion technique can handle any type of pile fabric range from short plush pile to shag pile construction and even needlefelts. With the machines developed by Gerber and by Justers the dye liquor is applied to the face of the carpet so that the liquor uptake by the jute backing can be controlled to some extent. The Gerber/Deep Dye "Unicolor" system of application consists of a driven drum covered laterally, with rubber ribbing. The slotted spaces between the ribs are filled from an adjustable dosing device, which allows the amount of liquor applied to be controlled depending on the type of carpet processed. Liquor pick-up varies between 100 and 250 percent. The carpet passes, pile down, through the nip between the driven drum and an upper roller. The pressure between the rollers requires adjustment according to the viscosity of the dye liquor and type of carpet to be dyed so as to ensure good colour penetration into the pile. It must not be too high, on the other hand, otherwise bar marks may be evident in the dyed carpet. This defect can occur more particularly on needle felts and for dyeing this type of floor covering the Gerber "Unipad" system is more suitable. This makes use of a tilting trough of very small volume in which runs of a soft rubber-coated roller. By tilting the trough the depth of immersion of the roller, and hence the amount of liquor picked up, can be controlled to suit the carpet being processed.
In contrast to all the foregoing techniques the Kuster system involves a two-stage application. The carpet is first impregnated with the necessary auxiliaries and chemicals (but no dye) by a conventional padding procedure using a swimming roller mangle. The liquor pick-up at this stage is about 100 percent. The carpet then passes to the dye applicator. This consists of a stainless steel roller rotating in a constant head of dye liquor in a trough. The speed of rotation and the viscosity of the liquor determine the liquor pick-up of the roller. A fibre glass doctor blade, running the full width of the roller then removes the dye liquor and allows it to flow down onto to the surface of the carpet passing, pile upwards, beneath. The additional liquor pick-up at this stage is about 300 percent, giving a total pick-up of 400 percent.
For dye fixation, steaming, without intermediate drying, is invariably used for reasons of economy and versatility. Saturated steam at 102.degree.-105.degree.C (215.degree.-220.degree.F) generally gives the best results with nylon and acrylic carpets since there is no tendency to drying-out, which might lead to dye migration to the tips of the pile nor does it give rise to water-spotting so long as the roof of the steamer is correctly designed. However, in order to ensure rapid heating of the carpet, which may contain as much as four times its weight of water on entering the steamer, the steamers may be equipped with pre-heating zones (e.g. infra-red heaters, or steam jet entry passages fed with superheated steam.) In steamers, not fitted with such pre-heating zones it may be preferable to give some degree of superheat to the steamer as a whole (e.g. by internal steam chests fed with pressure steam), giving a temperature (dry bulb thermometer) of 120.degree.-130.degree.C (250.degree.-265.degree.F). For polyester carpets the use of a superheated steam atmosphere of this type is necessary in order to obtain sufficiently rapid dye diffusion with the relatively short steaming times employed.
The type of steamer recommended varies, but in all cases the main requirement is that the pile of carpet does not come into contact with rollers which might cause distortion of the pile and marking-off. Festoon steamers are most favoured (Kusters, Kleinewefers, B.D.A. machines) but spiral (Gerber) and horizontal steamers (Stalwart machine) are also used. The rollers in the steamers should be driven and, particularly in festoon steamers, the drives should be independent and controllable to maintain constant loop lengths.
A further unit available, but not so far described owing to the absence of published information on the precise impregnation method is that produced by Fleissner. This utilizes their well known drum principle. The steaming chamber consists of a perforated drum steamer combined with a festoon steamer, or of a series of three perforated drum steamers. The advantage of drum steamers is that the steam is circulated right through the carpet and they do not rely so much on heat transfer from the upper and lower surfaces of the carpet - an advantage with deep pile constructions.
Any subsequent wet treatments are carried out on open width continuous washing ranges, with a variety of refinements to produce interchange between the liquor in the tanks and that in the carpet. Cold water is usually employed because of the relatively large volumes required, and conservation of water may be achieved by counter-current flow or recirculation systems. Thus the Justers unit employs tangentially running ribbed rubber belts to achieve a fast water current past the carpet in the washing tanks, between which are fitted squeeze rollers. The Stalward and Beloit-Kleinewefers machines use counter-current wash tanks with spray pipes and light squeezing between the tanks. The Fleissner unit, on the other hand, employs the drum washer principle.
One good type of washing off system in the Gerber "Rotomat" This is designed to obtain highly efficient washing off in the minimum space and uses an alternating wash/squeeze sequence with fresh wash liquor being supplied after each squeeze.
Because of the large quantity of water retained by carpets after wet treatments, drying is relatively expensive and as much water as possible must be removed mechanically prior to drying. Mangling, whilst being the most efficient can distort the pile, although the provision of rotary beaters prior to the drier will minimize this effect. An alternative method which does not cause pile distortion is to pass the carpet over an efficient vacuum suction slot. A wide variety of drying machines suitable for carpets are now available, mainly of the stenter type (sometimes with steam heated drum pre-driers).
In summary, the techniques that have been employed in prior art continuous dyeing techniques have always utilized the dyeing medium in the liquid state.
In the dip-pad type process both the dye and the chemicals for treating the fabric are applied at one station or position. However, it should be noted that the dye and the chemicals are applied in the liquid state.
In the Kuster process the chemicals for treating the fabric are applied at a first station by squeezing and the dye is applied at a second station. Here again, both the chemicals and the dye that are applied are in a liquid state.
Furthermore, all of the prior art processes depended on a foaming action occurring within the steamer.
In those prior art processes that employ compression in the application of dye, dealing with a fabric piece in excess of 12 feet resulted in variations in the finish of the resulting product.
The dyeing process of the present invention affords the first system in which the dye chemical mixture is applied in foam form in one application. The present invention can attain higher ratios of weight of dye pick-up to the weight of fabric to be dyed affording a range from 2 to 5 ratio. Whereas, prior art methods or processes afforded approximately 3 lbs. of paste pick-up to 1 lb. of fabric to be dyed.
The method of the present invention therefore, can incorporate more dye if desired and do so with less waste, since there is no waste of chemicals or dye in the steamer. Also, by virtue of the fact that the dye is applied to the fabric or material to be dyed in foam form the dye is in a more dispersed state affording for a faster heat up and fixation of the dye within the steamer thereby reducing the danger of migration of dye to the tips of the pile and avoids the problem of any over foaming inside of the steamer. Also, the steamer and wash-box arrangement of the present invention affords for a more gradual cool-down thereby conserving the steam requirement.
The present invention offers simplicity of application of chemicals and dyes while affording better pick up control when processing shag and plush type fabrics. The control of pick up produces even distribution over the fabric insuring full penetration into the fabric.
Since in the present process the dye is applied in foam form all tufts are saturated with highly dispersed foam, thereby, reducing the heat up time upon entering the steamer as compared to the prior art. This affords for faster fixation rates.
Furthermore, since the foam is already generated before entering the steamer, this system encounters no problem in handling synthetic primary backing where sylicones may inhibit foam formation after entering the steamer. The present process is also adaptable to shorter runs that utilize in the neighborhood, some 7 to 10 rolls. In addition, the turn-around-time (set up for a different run) is reduced because of the simplicity of the apparatus and method employed.